This invention relates to systems, compositions, and methods directed toward treating Huanglongbing, also known as HLB or citrus greening disease. More specifically, the invention relates to compositions that address the bacteria causing the disease and do not require the use of pesticides nor mechanical penetration of the bark periderm.
Citrus greening disease is a bacterial plant disease that is spread from one citrus tree to the next by a small insect called the Asian citrus pysllid. The bacteria, phloem-limited Liberibacter asiaticus, is a gram negative bacteria that travels throughout the tree's system and begins to destroy the fine roots of the tree (and therefore the tree's vascular system), making the tree unable to maintain its tree canopy. As the disease progresses, the tree's leaves begin to yellow on one side more than the other and become as small as mouse or rat ears, the tree produces small and lopsided fruit, and the fruit prematurely drops from the tree. If left untreated, the tree eventually dies.
To date, there is no cure or effective treatment for citrus greening disease. Most treatments involve a combination of spraying an insecticide like carbaryl, imidacloprid and aldicarb to kill the Asian citrus pyslli and micronutrients such as manganese and boron directly on the leaves. Potassium salicylate can also be applied. However, academic studies have not shown that enhanced foliar nutrition does anything to counteract the disease. As soon as the treatment is stopped, the symptoms return. Additionally, the insecticides can find their way into consumer products like orange juice and pose a risk to consumer health.
Other treatments require injecting an antibiotic like tetracycline and penicillin into the trees. Sometimes the tetracycline is used alone or followed by the penicillin. Other times the tetracycline is combined with soluble copper or zinc sulfate. Regardless, the treatment usually occurs two or more times at regular intervals and comprises trunk integrity. Injection requires drilling a hole into the tree about half the depth of the tree's trunk diameter, installing an injection screw into the hole, and coupling a supply hose to the screw. After treatment the hole is sealed. Drilling might be a good way to get antibiotics and insecticides into the phloem and xylem of a tree. However, it is labor-intensive, weakens the trunk, and leaves the trunk vulnerable for another bacteria, fungus, or insect to enter the trunk at a later time.
Some other treatments involve injecting the trunk or drenching the soil of non-bearing trees with chelated copper formulations such as MAGNA-BON® Agri-San soluble copper sulfate pentahydrate (Magna-Bon II LLC) and COP-R-QUIK® soluble copper (Natural Ag Solutions, LLC). Treatments must be done at three-month intervals over more than one growing season.
Copper is a very good bacteriacide for a lot of different ailments in a wide range of plants, so is zinc, manganese and any nutrient that has sulfate in it. However, in most orange groves the copper levels in the soil test are extremely high because of the copper's continual use.
Other solutions take a genetic route and seek to provide a more sustainable root stock or strain that is immune to the gram-negative bacteria. In the meantime, until the gram bacteria is killed and the roots restored, the symptoms keep reoccurring. including loss of fine feeder roots which leads to tree canopy loss and small, oblong fruit that falls prematurely off the tree.